A conventional wireless communications system may generally comprise a set of “mobile stations,” typically mobile stations are the endpoints of a communication path, and a set of “base stations,” (also known as “repeaters” or “base radios”) typically stationary and the intermediaries by which a communication path to a mobile station (MS) may be established or maintained. In such an environment and as is known in the art, the wireless communications system is termed “conventional” to denote the lack of a central controller to manage the communications between the MSs and the base stations. One such type of conventional wireless communications system utilizes time division multiple access (TDMA) to carry the communications of the system over a radio medium (also termed “spectrum”) that is divided into time slots and such a system is termed a conventional TDMA communications system.
In a conventional TDMA communications system, each base station (BS) provides synchronization for the MSs, so that the MSs can utilize the spectrum for communication. Once synchronization between the BS and MSs is obtained, each MS can properly receive control signaling that identifies the temporal position of each time slot within the spectrum and the time slot of the spectrum each MS can utilize for communications. Because the spectrum is often shared, the BS normally de-keys when the spectrum is not in use. As is known in the art, de-key (and conjugations of “de-key”) means that the BS's transmitter is turned off. Further known in the art, de-keyed means that the BS's downlink is inactive while the BS's uplink remains active and available to detect MS transmissions. When the BS is de-keyed, even though the BS is able to detect transmissions from the MS, the BS may not be able to process the transmissions because the MS may not be in synchronization with the BS. Thus, when the BS is de-keyed, a MS can not utilize the BS for communications until a) the MS sends a wakeup message to the BS which causes the BS to re-key and b) the MS synchronizes to the BS to receive timing information about the BS. After the wakeup and synchronization processes are completed, then a MS may finally utilize the BS for communications.
If the MS believes that the BS is de-keyed (e.g. due to not timely receiving synchronization), then the MS transmits the wakeup message and attempts to synchronize, which takes extra time and thus is undesirable if the MS has to send a wakeup message prior to every transmission. If the MS believes that the BS is keyed (e.g. due to timely receiving synchronization), then the MS does not transmit the wakeup message. In a conventional TDMA communications system, the MS is not explicitly notified that the BS has de-keyed. That is, there is no message that is sent from the BS to the MS that notifies the MS that the BS is about to de-key, de-keying or is de-keyed. In a conventional TDMA communications system, the MS indirectly determines that the BS has de-keyed, such as by not detecting synchronization from the BS. However, there is a finite amount of time that passes before the MS realizes that the BS has de-keyed and during this finite amount of time, if the MS sends communications to the BS, then the communications sent to the BS are ignored by the conventional TDMA communications system since (as mentioned above) the BS requires that the wakeup and synchronization processes be completed before the MS may utilize the de-keyed BS for communications.
Ignoring communications is a problem because the user of the MS does not have knowledge that the communications have not been received by the intended recipient of the communications. For example, if an emergency communication is placed by emergency personnel, as a user of a MS, and the BS is de-keyed, then the emergency personnel is not aware that the emergency communication has not reached its intended recipient, e.g. emergency personnel at a police station. In any case, ignoring communications is a problem.
Accordingly, there is a need for an improved method of accessing a de-keyed base station in a conventional TDMA communications system.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.